At the present, in the laws of various countries and regions and in the NCAP (New Car Assessment Program), collision of automobiles is being regulated and assessed. Among these, in recent years, in addition to the protection of the heads of pedestrians, studies have been advanced regarding protection of the legs (see “European Enhanced Vehicle-safety Committee, Improved Test Methods to Evaluate Pedestrian Protection Afforded by Passenger Cars”, EEVC Working Group 17 Report, December 1998 etc.) Demand is rising for protection of the legs at the time of a collision between a pedestrian and an automobile.
In automobiles up until now, attempts have been made to design bumpers with impact resistance predicated on collision with other objects or other vehicles. However, when such a designed automobile collides with a pedestrian, there is a good chance of causing residual disability to the knee tendons and shin bones of the pedestrian's legs. For this reason, design of bumpers for reducing such problems is being sought.
As a measure for solving this, provision of a plastic absorber between the bumper fascia and reinforcement to absorb the impact energy generated at the time of collision with a pedestrian is disclosed in Japanese Patent Publication (A) No. 2004-322861 (Document 1).
Further, regarding a metal hat-shaped cross-sectional shape, as a vehicular collision reinforcement (bumper reinforcement), to prevent the web from buckling, a shape making the thickness of the web greater than the flange thickness of the center is disclosed in Japanese Patent Publication (A) No. 2005-178695 (Document 2).
Furthermore, in an automobile bumper beam, for the purpose of increasing the amount of energy absorbed at the time of a frontal collision, a structure provided with a front base sheet and a rear base sheet made of a metal material, two metal cores arranged vertically between these, and an energy absorber made of a metal material, the two cores provided with continuous projections and recesses extending in the front-back direction of the chassis, is described in Japanese Patent Publication (A) No. 2003-503272 (Document 3).
For an absorber provided between a fascia and a bumper beam and believed to be plastic, an energy absorber (absorber) having an upper horizontal part and lower horizontal part provided with continuous projections and recesses extending in the front-back direction of the chassis and an intermediate horizontal part connecting these, the upper horizontal part and lower horizontal part having an upper front nose part and lower front nose part extending out to the front of the intermediate horizontal part, is described in Japanese Patent Publication (A) No. 2005-534555 (Document 4).
Further, a plastic pedestrian-use energy absorber having, as one type of the projections, a plurality of collapsible lobes each comprised of a front lobe part with a small cross-sectional area and a rear lobe part with a large cross-sectional area in the front-back direction of the chassis and having a cross-sectional approximately hat shape is described in Japanese Patent Publication (A) No. 2005-536392 (Document 5).
Further, in a bent sheet used as a roofing material, a roll former forming a metal strip into a hat-shaped cross-sectional shape and producing a member having wave shapes of alternately repeating recesses and projections along the width direction along the longitudinal direction of the member is described in Japanese Patent Publication (A) No. 10-175020 (Document 6).
Further, a front structure of a vehicle comprised of a flared top energy absorber not having projections and recesses in the front-back direction of the chassis, but having bent parts in the middle of the front-back direction of the chassis and produced by press-forming a steel sheet and a bottom energy absorber with a front end part positioned to the rear from the top energy absorber is described in Japanese Patent Publication (A) No. 2006-232042 (Document 7).
However, for example, the plastic absorber disclosed in Document 1 requires a large amount of deformation and residual crush in absorbing the impact energy. For this reason, the plastic absorber body becomes larger, the dimensions between the bumper fascia and reinforcement become larger, and the minimum turning radius of the vehicle is increased. This is also not preferable in terms of aesthetic design. Further, the plastic absorber is one cause of a high material and production cost and deterioration of the cost of the vehicle as a whole.
Further, the bumper reinforcement disclosed in Document 2 strengthens the web so as to prevent web buckling and locally increase the absorbed energy at the time of collision, so from the viewpoint of pedestrian protection, conversely the pedestrian may be given greater injury, so this is not preferable.
Furthermore, the projections or recesses disclosed in Document 3 are shapes for enabling the sheet thicknesses of the two cores to be made thinner and simultaneously maintaining resistance to buckling (see Description, paragraph no. 0023). Again, from the viewpoint of pedestrian protection, conversely the pedestrian may be given greater injury, so this is not preferable.
Further, the invention disclosed in Document 4 absorbs relatively low energy by making either of the upper horizontal part or lower horizontal part move upward. However, the energy absorption by plastic deformation of a plastic, as explained later, is small at the initial period of deformation, so at the time of collision with a pedestrian at a speed of 40 km/hr, it is not possible to protect the pedestrian by a short stroke. The structure is also complicated, so there is the problem that this is not preferable in terms of aesthetic design.
Further, the invention disclosed in Document 5 is also a plastic, so in the same way as the invention disclosed in Document 4, when a pedestrian is collided with at a speed of 40 km/hr, there are the problems that the pedestrian cannot be protected by a short stroke and the impact energy cannot be absorbed by a small stroke.
Further, the invention disclosed in Document 6 has as its object to facilitate the plastic deformation of a roofing material to a curved state. Neither application of use for an automobile bumper absorber nor the problem of absorbing the impact energy received from the leg of a pedestrian is described.
Further, the invention disclosed in Document 7 is a complicated structure not having projections and recesses in the front-back direction of the chassis, but having a top energy absorber and bottom energy absorber, so has problems similar to Document 4.